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(No Model.)

(J. E. CARPENTER.

' PROCESS OF MAKING RESISTANCE PLATES. No. 511,407. Patented Dec. 26, 1893.

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UNITED STATES PATENT OFFICE.

CHARLES E. CARPENTER, OF BRIDGEPORT, CONNECTICUT, ASSIGNOR TO THE CARPENTER ENAMEL RHEOSTAT COMPANY, OF SAME PLACE.

PROCESS OF MAKING RESISTANCE-PLATES.

SPECIFICATION forming part of Letters Patent No. 511,407, dated December 26, 1893.

Application filed February 7, 1893. Serial No. 461,321. (No specimens.)

To (all whom it may concern.-

Be it known that I, CHARLES E. CARPENTER, a citizen of the United States, and a resident of Bridgeport, in the county of Fairfield and State of Connecticut, have invented certain new and useful Improvements in Processes of Making Resistance-Plates for Use in Connection with Electrical Apparatus, of which the following is a specification.

This invention relates to improvements in the process of making resistances in which the conductor is embedded in an insulating material such as enamel which at the same time holds the conductor to a suitable support, and has for its object to simplify the methods already existing and introduce certain steps whereby a new and improved instrument is produced.

The drawings show the condition of a resistance plate at several stages of the process as subsequently described.

Figure 1. shows a vertical cross section of a portion of a support A with an enamel coating B. Fig. 2. shows a vertical cross section of the same, but after an upper coat G and conductor 0 have been applied. Fig. 3. is a plan on a reduced scale showing one form of the conductor and how it may be distributed upon the plate. i

In carrying out my process I first apply to the surface of a plate suitable for support, which is preferably a good conductor of heat, a coat of enamel; then fuse the same so that it adheres firmly to the surface of the plate. This produces what is shown in section in Fig. 1. Having shaped by bending or otherwise, an electrical conductor, copper for instance, so that it has a curved or reflex form, I then apply the same to the surface of the enamel B after it has become sufficiently hard. The conductor C is buried in an upper coating of enamel G applied to the first coat already fused, said second coating having a lower fusing point than the first coat, and then the whole is raised to the fusing point of this second coat, whereupon this second coating G becomes attached to the first coating B and thereby securely holds and perfectly insulates the conductor C. This product is then cooled and is complete, as far as this process is concerned. It is obvious that, if the second coating is not sufficiently thick, additional coatings may be applied. The completed product is shown in Fig. 2.

By the expression, shaping the electrical conductor so that it has a curved or reflex form, I mean so that it has practically no straightparts ofany considerable length. The purpose of this will be pointed out later.

One of the important steps of this invention is to have the first coat of enamel fuse at a higher temperature than the second coat, so that the first coat does not become fused during the fusing of the second or subsequent coats,thus avoiding the danger of having the conductor penetrate the said first coat and contact with the base plate. It is obvious that where the first and subsequent coats fuse at the same temperature the conductor is liable to penetrate the first coat while in a soft condition when fusing the second or subsequent coats. The shaping of the conductor is also one of the important steps of this process. Aside from the obvious advantage of being put into any desired form so as to be distributed through the enamel, the curving has the very important function of distributing the strain caused by the unequal expansion and contraction of the embedded conductor and the enamel, both while the resistance plate is being manufactured and when the instrument is in use. By using aconductor no part of which is straight, or the straight part of which is very short, the expansion or contraction of the conductor places a strain upon the enamel in every direction. \Vhere the conductor has substantially no straight portions the actual difference between the linear expansion of the conductor in any one direction and the corresponding expansion of the enamel is so slight that it is immaterial. By distributing the strain as above described, cracking is avoided which would happen if the strain were in a straight line for some distance.

I wish it to be understood that the improvement consisting in applying coatings having different fusing points and the improvement consisting in curving the conductor prior to embedding it in the enamel do not of neces- ICO having a fusingpoint lower-than the enamel already applied and raising the whole to a temperature suflicient to fuse said second layer of enamel, substantially as described.

2. The improvement in the method of constructin g resistances which consists in attaching to a suitable support a coating of enamel by fusing the same, having shaped a conductor into curved or reflex form, placing said conductor upon the surface of the coating, covering the same with a coating of enamel having a fusing point lower than the enamel already applied,and raising the whole to atemperature sufficient to fuse said second layer of enamel, substantially as described.

3. The improvement in the method of constructing enamel coated resistances for the conversion of electrical energy into heat which consists in applying a coating of enamel to a suitable support, bending a conductor of electricity into curved or reflex form, applying the same to the surface of the enamel applying a second coating of enamel having a lower fusing point than the first coating and fusing the same to form a compact mass, substan- 4o Witnesses:

J. H. DELANY, W. H. MOTT. 

